1. Technical Field
Exemplary embodiments of the present invention relate to communication networks that enable data transmission to mobile terminals and a method of transmitting data to such a mobile terminal.
2. Description of Related Art
Two recent growth trends in the fields of communications and information technology have been the use of mobile communications, especially mobile telephony, and the use of computer networks such as the internet to share and exchange data. These two trends are set to continue and also to converge. In 2000 the Universal Mobile Telecommunications System (UMTS) will be launched in Europe and this is intended to provide both fixed and cellular mobility across a single network infrastructure, supporting a full range of mobile communications capabilities from short messages, high quality speech to full interactive multi-media communications. Some of the challenges that must be addressed in order to realise UMTS are the provision of user terminals, wireless network infrastructures to provide the necessary bandwidth for mobile users and network flexibility to allow users to connect simultaneously to a number of networks (including both fixed and mobile networks) and for those network connections to be seamlessly dropped and added as a user moves out of, or into, the range of a network.
It is known (see ‘Flexible Network Support for Mobility’, X Zhao, C Castellucia & M Baker, MOBICOM 98, Dallas, Tex., pages 145-156) how to provide support for a mobile terminal using a number of wireless communication networks. Because of the mobility of the host, the network connectivity of the host, and hence its network address, will keep changing. Hosts communicating with the mobile terminal therefore send data to the mobile terminal's ‘home’ network address and this data is intercepted by a fixed host, called a home agent, which is connected to the ‘home’ network of the mobile terminal. The mobile terminal is in communication with the home agent so that the home agent is always aware of the network address of the mobile terminal (or network addresses if the mobile terminal is connected to more than one network), enabling the home agent to forward data packets for the mobile terminal to the mobile terminal. If the mobile terminal is connected to a number of networks and is receiving different types of data flow (e.g. file transfer, WWW (World Wide Web) downloads, voice, etc.) then the mobile terminal will inform the home agent of the different networks to which it is connected and also instruct the home agent which network to use for each different data flow.
According to a first aspect of the invention there is provided a method of transmitting one or more data streams to a mobile terminal having multiple network connections, the method comprising the steps of;
(i) sending the one or more data streams from a correspondent host to a home agent located in the home network of the mobile terminal, the mobile terminal sending a request for the data stream to be transmitted by the correspondent host and the mobile terminal communicating with the home agent to transmit the network location of the mobile terminal to the home agent; and(ii) forwarding the one or more data streams to the mobile terminal, characterised in that the mobile terminal communicates network connectivity data to the home agent and that the forwarding of the one or more data streams is dependent upon the network connectivity data received by the home agent.
One advantage of exemplary embodiments of the present invention is that the routing of the data to the mobile terminal is performed by the home agent rather than the mobile terminal, making the terminals less complex, which should lead to smaller, cheaper terminals which have lower power consumption.
A terminal has a network connection if it is in communication with a network, regardless of whether or not the terminal is transmitting or receiving data via the network connection.
Furthermore, in response to a change in the network connectivity data received by the home agent at least one of the data streams may be forwarded by the home agent to a network cache, said at least one data stream(s) being stored in the network cache until the home agent forwards said at least one data stream(s) to the mobile terminal. Requests sent by the mobile terminal to the correspondent host may be sent via the home agent. Additionally, all communication from the home agent to the mobile terminal and/or all communication from the mobile terminal to the home agent may be routed via a foreign agent, the foreign agent being located in a subnetwork to which the mobile terminal is connected. In response to a change in the network connectivity data received by the home agent the information content of at least one of the data streams may be reduced before being forwarded to the mobile terminal. The reduction of information content of the at least one of the data stream(s) may comprise the conversion from a first data format to a second data format having a lower resolution than the first data format. For example, this could be the conversion of a stereo audio signal to a mono audio signal, or a the conversion of a colour video signal to a black and white colour signal.
According to a second aspect of the invention there is provided a mobile communications terminal comprising an interface to a plurality of networks; means for transmitting and receiving data using some or all of the network interfaces; and control means operative to send messages concerning the availability of communications paths to the mobile terminal via at least one of said plurality of network interfaces. The terminal may have one interface which connects to a plurality of networks, for example a PCMCIA card which comprises GSM, PSTN and ISDN modems, or a number of interfaces which can each connect to one or more networks.
According to a third aspect of the invention there is provided a communications network comprising; a plurality of mobile communications subnetworks, some of said mobile communications subnetworks having overlapping geographical coverage; and control means operative such the mobile terminals can each be in simultaneous communication with more than one of the plurality of mobile communications subnetworks; characterised in that the control means receives network connectivity data from each mobile terminal and routes data streams to each mobile terminal on the basis of the received network connectivity data from that terminal.
According to a fourth aspect of the invention there is provided a Mobile IP extension comprising an Extension field and a Length field and characterised in that the Mobile IP extension further comprises a Network Type Field and a Care-of-Address field. There is also provided a Mobile IP registration packet, characterised in that the Mobile IP registration packet comprises one or more Mobile IP extension(s) as described above. There is additionally provided a signal comprising a Mobile IP registration packet as described above.
An exemplary embodiment of the present invention also provides a communications system for effecting data transfer from a first computer, attached to a communications network, to a mobile communications terminal which has an allocated home address in the communications network and a home agent to manage communication between data sources in the communications network and the mobile terminal when the terminal is not at its home address, wherein; the mobile communication terminal is configured for simultaneous communication via a plurality of types of wireless communications channels; characterised in that the mobile terminal sends to its home agent information about the current availability of the different communications channels, the home agent selecting the appropriate communications channel in accordance with the type or characteristics of data to be communicated to the mobile terminal.